Reflection Cancellation Research Articles

Enabling data-driven and bidirectional model development in Verilog-A for photonic devices

We present a method to model photonic components in Verilog-A by introducing bidirectional signaling through a single port. To achieve this, the concept of power waves and scattering parameters from electromagnetism are employed. As a consequence, one can simultaneously transmit forward and backward propagating waves on a single wire while also capturing realistic, measurement-backed responses of photonic components in Verilog-A. We demonstrate examples to show the efficacy of the proposed technique in accounting for critical effects in photonic integrated circuits such as Fabry-Perot cavity resonance, reflections to lasers, reflection cancellation circuits, etc. Our solution makes electronic-photonic co-simulation more intuitive and accurate.

Ultra-wideband RCS reduction based on reflection cancellation and tunable absorption

Ultra-wideband RCS reduction based on reflection cancellation and tunable absorption

Grating design methodology for laser cooling

We present a design strategy for grating magneto-optical traps (GMOTs). It takes the three most relevant optical properties for laser cooling (radiation pressure balance, specular reflection cancellation, and diffracted polarization) to build a scalar figure of merit. We use a rigorous coupled wave analysis (RCWA) simulation to find a geometry that maximizes this figure of merit. We also introduce a criterion that takes into account the robustness of the manufacturing processes to select a geometry that is reliable to manufacture. Finally, we demonstrate that the fabricated grating exhibits the expected optical properties and achieves typical GMOT performance.

A novel approach to interface high-Q Fabry–Pérot resonators with photonic circuits

The unique benefits of Fabry–Pérot resonators as frequency-stable reference cavities and as an efficient interface between atoms and photons make them an indispensable resource for emerging photonic technologies. To bring these performance benefits to next-generation communications, computation, and time-keeping systems, it will be necessary to develop strategies to integrate compact Fabry–Pérot resonators with photonic integrated circuits. In this paper, we demonstrate a novel reflection cancellation circuit that utilizes a numerically optimized multi-port polarization-splitting grating coupler to efficiently interface high-finesse Fabry–Pérot resonators with a silicon photonic circuit. This circuit interface produces a spatial separation of the incident and reflected waves, as required for on-chip Pound–Drever–Hall frequency locking, while also suppressing unwanted back reflections from the Fabry–Pérot resonator. Using inverse design principles, we design and fabricate a polarization-splitting grating coupler that achieves 55% coupling efficiency. This design realizes an insertion loss of 5.8 dB for the circuit interface and more than 9 dB of back reflection suppression, and we demonstrate the versatility of this system by using it to interface several reflective off-chip devices.

Motor Overvoltage Mitigation by Active Cancellation of Reflections Using Parallel SiC Devices With a Coupled Inductor

Motor Overvoltage Mitigation by Active Cancellation of Reflections Using Parallel SiC Devices With a Coupled Inductor

Millimeter-Wave High-Gain Dual-Polarized Flat Luneburg Lens Antenna with Reflection Cancellation

Because of its good beam coverage and beam scanning abilities, the Luneburg lens (LL) is a promising multibeam antenna for the fifth-generation (5G) wireless communications. However, the conventional LL has a spherical formfactor, exhibiting a large volume, large weight, and curvature surface, all of which limit the adoption of an LL in practice. To alleviate the problem, a flat LL is proposed, with transformation optics to convert the conventional spherical structure into a flat one. However, a high permittivity distribution is usually required in a transformed flat LL, causing of server reflections, which further degenerates the performance of the LL in terms of both gain and efficiency. In this article, a millimeter-wave dual-polarized flat Luneburg lens antenna (FLLA) is proposed following the transformation of optics, and implemented using multilayer PCBs, where a reflection cancellation method is introduced to optimize the multilayer structure to improve its gain and efficiency. The designed FLLA is exemplified in the Ka-band and fed using a dual-polarized patch antenna. The measured results show that the designed FLLA has an impedance bandwidth (|S11| ≤ −10 dB) of 27.5–32.6 GHz, a gain of 16.8–18.8 dBi over the operating band, and a beam scanning range up to ±25°/±24° with a gain loss of 1.72 dB/1.7 dB in either E- or H-plane, respectively.

Compact asymmetric treatments for perfect sound absorption in ventilated problems

This presentation introduces compact asymmetric treatments for sound absorption, i.e., simultaneous cancellation of reflection and transmission, in a lined duct of constant cross section. The treatments are composed of side by side and sub-wavelength resonators. They are thus compact, which facilitates their practical use. The simplest asymmetric treatment is formed by a pair of detuned resonators that can lead to a perfect monochromatic sound absorption. Furthermore, the combination of multiple pairs of resonators generates multiple low quality factor absorption peaks leading to an absorption plateau. Two compact asymmetric treatments are presented: one is composed of quarter-wavelength porous resonators to prove their ability to achieve perfect sub-wavelength absorption in a duct problem and the other is composed of Helmholtz resonators flush mounted on the walls of a large cross-section duct. In both cases, the evanescent coupling between the resonators has an important impact on the treatments behavior and is thus accounted for during their optimization. The experimental results are found in good agreement with the theory and a mean absorption coefficient of 99% over a large target and subwavelength frequency range is observed for each treatment.

Simulation of Active Echo Cancellation Effects Using the ARCS Concept

Active echo cancellation is an efficient method for reducing the target detected probability. The radar cross section (RCS) of the target detected by radar after using the active echo cancellation method is defined as the active radar cross section (ARCS). The ARCS concept, which may be used to evaluate reflection of the target under the effect of multiple antennas, is employed to design and achieve echo cancellation. In this paper, numerical simulation for active echo cancellation using antennas is designed. The direction of the radiation source is obtained by means of dual antenna angle measurement. Active echo cancellation is implemented by adjusting the radiation power and phase of the echo cancellation antenna. By using the proposed dual antenna structure, ARCS in the direction of the object facing the radiation source and its vicinity is significantly reduced. In addition, the effect of antenna position on reflection cancellation is discussed. From these simulation results, we conclude that the proposed method is efficient in reducing the target scattering intensity. Such investigation can be extensively applied into designing active echo cancellation strategies.

Impact of source and receiver distributions on imaging of dipping reflectors with passive reflection seismic interferometry

SUMMARY Passive reflection seismic interferometry (PRSI) facilitates imaging the subsurface structure using passive sources but according to the general theory, the target needs to be illuminated equally from all directions to obtain a kinematically correct result. In practice, this requirement is almost impossible to meet which can introduce artefacts into the PRSI results. Our study was motivated by an unsuccessful attempt to image a couple of known dipping reflectors by applying PRSI to a data set of local microearthquakes clustering around the glacially triggered Burträsk fault. Dipping reflectors are a special case since they introduce a directionality into the seismic-interferometry problem that makes the results especially sensitive to the source azimuths. To investigate which source distributions are favourable in such a case and to study the range of artefacts occurring, we analyse a number of acoustic and elastic synthetic data sets calculated using a simple model of a dipping fault. Our results show that the main contribution for imaging such a fault with PRSI comes from sources in the hangingwall whereas contributions from the footwall are often weak and kinematically incorrect. The type and position of the occurring artefacts depend upon both the source azimuth and the type of modelling. In the acoustic case, the main artefact is a gently dipping reflection caused by insufficient cancellation of the direct reflection at the fault. In the elastic case, the artefacts are dominated by a set of both gently and steeply dipping reflections related to P–S converted waves. These artefacts are present even for ideal illumination due to the use of source records containing both P- and S-wave contributions. During interpretation, it is essential to be able to distinguish between physically meaningful reflections and artefacts. We found that both acoustic and elastic artefacts stack best at lower than expected normal moveout velocities. If data quality is insufficient for velocity analysis, our results can serve as a reference point for the interpretation of dipping features in PRSI images.

Controlling Graphene Sheet Resistance for Broadband Printable and Flexible Artificial Magnetic Conductor-Based Microwave Radar Absorber Applications

Current artificial magnetic conductor (AMC) designs use metallic patterns on rigid substrates and focus on shapes and sizes of AMC structures, rather than on material performance, which has hindered operation bandwidth and design flexibility. Here, we introduce printed graphene AMC-based broadband and flexible microwave radar absorbers, which not only redirect but also absorb the incident wave so to broaden the operation bandwidth. Contrasting to other reported works, the phase characteristics of the AMCs are realized through the control of the surface resistance provided by printed graphene laminates. We produced a variety of AMC structures, composed of printed graphene circular ring arrays with exactly the same shape and size, but different sheet resistances. By carefully designing the sheet resistance of printed graphene laminates, the optimized anti-phase reflection cancellation between AMCs can be achieved. With printed graphene AMCs and flexible dielectric substrate, the absorber presented in this work has a broadband effective absorption (above 90% absorptivity) from 7.58 GHz to 18, is polarization insensitive under normal incident, and can work at relatively wide incident angles. Furthermore, this absorber is capable of bending easily with notable performance, which makes it ideal for applications with irregular and uneven shapes.

A High Gain Series-Fed Circularly Polarized Traveling-Wave Antenna at W-Band Using a New Butterfly Radiating Element

We propose a novel series-fed circularly polarized (CP) traveling-wave antenna known as the “Butterfly” antenna suitable for operation at the millimeter-wave frequencies. The Butterfly unit-cell consists of a sequentially rotated series-fed linear array of four microstrip patch antennas. The proposed CP Butterfly structure offers low cross-polarization radiation and wide axial ratio (AR) beamwidth. A periodic leaky-wave antenna (LWA) analysis provides insights into the radiation characteristics of the Butterfly series-fed linear array antenna, which is validated by the full-wave electromagnetic simulations. The open-stopband (OSB) is suppressed in the broadside direction due to the cancellation of the internal reflections within each cell of the sequential-phase fed linear array. The measured and the simulated AR, radiation patterns, and gain are presented for the broadside radiation of the parallel–series fed $8\,\,\times24$ and $32\times24$ planar array antenna at 86 GHz. The average measured 3 dB gain beamwidths are 9.5° and 2.9° along the $\phi = 0^{\circ }$ plane of the $8\,\,\times24$ and $32\times24$ planar array antenna, respectively.

Motion of a Legged Bidirectional Miniature Piezoelectric Robot Based on Traveling Wave Generation.

This article reports on the locomotion performance of a miniature robot that features 3D-printed rigid legs driven by linear traveling waves (TWs). The robot structure was a millimeter-sized rectangular glass plate with two piezoelectric patches attached, which allowed for traveling wave generation at a frequency between the resonant frequencies of two contiguous flexural modes. As a first goal, the location and size of the piezoelectric patches were calculated to maximize the structural displacement while preserving a standing wave ratio close to 1 (cancellation of wave reflections from the boundaries). The design guidelines were supported by an analytical 1D model of the structure and could be related to the second derivative of the modal shapes without the need to rely on more complex numerical simulations. Additionally, legs were bonded to the glass plate to facilitate the locomotion of the structure; these were fabricated using 3D stereolithography printing, with a range of lengths from 0.5 mm to 1.5 mm. The optimal location of the legs was deduced from the profile of the traveling wave envelope. As a result of integrating both the optimal patch length and the legs, the speed of the robot reached as high as 100 mm/s, equivalent to 5 body lengths per second (BL/s), at a voltage of 65 Vpp and a frequency of 168 kHz. The blocking force was also measured and results showed the expected increase with the mass loading. Furthermore, the robot could carry a load that was 40 times its weight, opening the potential for an autonomous version with power and circuits on board for communication, control, sensing, or other applications.

One-Pot Synthesis of Doped-Polypyrrole/Fe₃O₄ Nanosphere Composites and Their Microwave Absorption Performance.

Doped-polypyrrole/Fe₃O₄ (D-PPy/Fe₃O₄) nanospheres were successfully synthesized via a onepot process. In this process, polyvinyl alcohol (PVA) plays an important role in the construction of polypyrrole nanoparticles, and Fe3+ ions were the oxidant and the only raw resource of Fe₃O₄. The morphology, magnetic properties, and electromagnetic microwave absorption properties of D-PPy/Fe₃O₄ composites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), a vibrating sample magnetometer (VSM) and a vector network analyser (VNA). The results indicate that D-PPy/Fe₃O₄ nanospheres become more disperse and regular due to the addition of PVA. The influence of the mass ratio of PVA to pyrrole on the microwave absorption performance of the D-PPy/Fe₃O₄ composites was also investigated. When the mass ratio of PVA/pyrrole was 0.75:1, the minimum reflection loss (RLmin) value of the D-PPy/Fe₃O₄ composites reached -41.3 dB at 7.7 GHz with a thickness of 3.0 mm. The microwave interference cancellation of interface reflection, nature resonance loss and current loss are the main reasons for the loss of electromagnetic microwaves for the as-prepared D-PPy/Fe₃O₄ composites.

Study on the characteristics of a V-shaped metamaterial absorber and its application

This paper proposed a V-shaped metamaterial absorber to enrich the structure of the absorber and improve its absorbing efficiency. The structure is to print an inclined V-shaped copper-plated layer on the FR4 substrate and arrange them periodically. The absorber has two large absorption peaks, and the bandwidth with an absorption rate of more than 90% is 1.3 GHz. The origin of absorption mainly comes from reflection cancellation, followed by dielectric loss. The basic type of V-shaped absorber has excellent promotion space and application prospects. It can further optimize and expand the performance of absorber through three main forms: unit nesting, multi-unit array and multi-layer stacking. Based on the structure of unit nesting combination, the processing of experimental samples and the measurement of electromagnetic parameters were completed. The experimental results are in good agreement with the simulation results.

Design of a Novel Microstrip Franklin Leaky-Wave Antenna Using the Eigenstate Approach

This paper presents the design of a novel periodic leaky-wave antenna (LWA) using modified microstrip Franklin unit cells. Two additional quarter-wave couple-line sections are used to allow the cell to work with the $n =-2$ fast-wave harmonic. It allows the use of low- $\epsilon _{\mathrm {r}}$ substrates so the designed LWA is cost-effective, can be easily integrated with radar front-end circuits, and avoids the excitation of surface waves. A novel application of eigenstate analysis leads to a simpler and more intuitive approach for the implementation of the reflection cancellation concept to eliminate open-stopband (OSB) effects. This is realized in the proposed structure with the use of a pair of interdigital fingers and different widths for the two lines forming the coupled section. A general design flow is also proposed for the design of the unit cell and LWA. Finally, a 40 cell LWA is fabricated on a Rogers 3003 substrate with $\epsilon _{\mathrm {r}} = 3$ . The measured results show that the beam scans continuously from −54° to +55° when frequency is varied from 54.7 to 70 GHz, and no visible OSB effect is observed near the broadside direction.

Research on visible light indoor positioning technique using two light sources andspecular reflection cancellation

Here, a high accuracy camera-based visible light indoor positioning system (IPS) has been investigated. A novel two LEDs-based positioning algorithm is proposed aiming at solving the problems of positioning ambiguity with a good trade-off between high accuracy and computational complexity. The simulation results show that the positioning errors of the proposed 2-LED positioning algorithm achieves 2 cm when the resolution of the image sensor (IS) exceeds 2500 pixels/line. A specular reflection cancellation scheme is presented to further reduce the positioning errors when specular reflection interference occurs. The simulation results show that the positioning errors can be reduced to 2.71 cm after using the specular reflection cancellation.

3D Printing Using a 60 GHz Millimeter Wave Segmented Parabolic Reflective Curved Antenna

This paper proposes a segmented parabolic curved antenna, which can be used in the base station of a 60 GHz millimeter wave communication system, with an oblique Yagi antenna as a feed. By analyzing the reflection and multi-path interference cancellation phenomenon when the main lobe of the Yagi antenna is reflected, the problem of main lobe splitting is solved. 3D printing technology relying on PLA (polylactic acid) granule raw materials was used to make the coaxial connector bracket and segmented parabolic surface. The reflective surface was vacuum coated (via aluminum evaporation) with low-loss aluminum. The manufacturing method is environmentally friendly and the structure was printed with 0.1 mm accuracy based on large-scale commercial applications at a low cost. The experimental results show that the reflector antenna proposed in this paper achieves a high gain of nearly 20 dBi in 57–64 GHz frequency band and ensures that the main lobe does not split.

Acoustic transducer design for active reflection cancellation in a finite volume wave propagation laboratory

This report describes the design, fabrication, and experimentally obtained electro-acoustic response of an acoustic transducer suite constructed for use in the Wave Propagation Laboratory (WaveLab) at ETH Zürich. WaveLab aims to immerse a physical acoustic experiment within a real-time numerical environment, by implementing exact boundary conditions (EBCs) [J. Acoust. Soc. Am., 134(6), EL492–EL498, (2013)]. When scale-model ultrasonic experimentation is not possible, a system with EBCs allows for low frequency, reflection-free acoustic measurements in a small physical domain. The physical experiment of the WaveLab facility consists of a water tank measuring only 2 m on a side, while WaveLab’s EBCs are realized through a massive computational engine coupled with a dense array of sensing and emitting acoustic transducers. The transducers are used to sense outgoing acoustic waves and to create a reflection-cancelling surface. Criteria for the transducers are discussed in terms of individual and overall system response. The design parameters and associated models include sensitivity, scattering strength, directivity, frequency response, noise floor, and the dynamic range of the system. The transducer designs and models are presented alongside their physical prototypes and experimental results.

Polarization-sensitive laser feedback interferometry for specular reflection removal.

Specular reflection from the surface of targets or prepared specimens represents a significant problem in optical microscopy and related optical imaging techniques as usually the surface reflection does not contribute to the desired signal. Solutions exist for many of these imaging techniques; however, remedial techniques for imaging based on laser feedback interferometry (LFI) are absent. We propose a reflection cancellation technique based on crossed-polarization filtering that is tailored for a typical LFI configuration. The technique is validated with three experimental designs, and a significant improvement of about 40dB in the ratio of the diffuse and specular LFI signal is observed. Applications of this principle extend from specular reflection removal to characterization of target materials in industrial to biomedical domains.

Cancellation of room reflections over an extended area using Ambisonics.

This paper investigates the compensation of room reflections based on Ambisonics. A multichannel room equalization method for Ambisonic playback systems is proposed. The compensation filters are designed to operate in the spherical harmonics domain, prior to the decoding step. Their design requires the inversion of a matrix which can be ill-conditioned at low frequencies and for higher Ambisonic orders. A crossover and cross-order method is proposed to circumvent this problem and to reduce the amount of necessary regularization. Simulation results are presented in frequency, space, and temporal domains over a wide-range of frequencies. It is shown that the proposed method is efficient and can reduce the reproduction error to -14 dB in the reconstruction area defined in free field. Practical considerations such as Ambisonic room response estimation and robustness of the method are investigated. Experimental results are provided and show good agreement with the theory. Finally, a glimpse into the extension of the proposed method to create three-dimensional measurement-based Ambisonic reverberation is discussed.